feat(pai.ts): passthrough unknown CLI flags to claude

[HyggeHacker]

Summary

PAI's arg parser silently dropped unrecognized flags (e.g., --plugin-dir, --mcp-config), preventing users from combining PAI with Claude Code's native flags. Unknown flags are now collected and forwarded to the underlying claude command, enabling use cases like:

pai -l --plugin-dir ~/Projects/boxie --mcp-config ~/.claude/mcp-profiles/boxie.json

Changes

• Unknown flags (args starting with -) are collected into a passthrough array instead of being silently ignored
• If the next arg after an unknown flag doesn't start with -, it's treated as that flag's value
• Non-flag unknown args still produce the existing error message
• The passthrough array is forwarded to cmdLaunch() and spread into the claude command args

Known limitation

Flags that accept multiple space-separated values (e.g., --add-dir dir1 dir2, --allowedTools Bash Edit Read) will only capture the first value. This covers the vast majority of Claude Code flags which take a single value. Multi-value flags can use repeated invocations (--add-dir dir1 --add-dir dir2) or = syntax as a workaround.

Test plan

• pai -l --plugin-dir ~/Projects/boxie — plugin-dir passed through correctly
• pai --mcp-config ~/.claude/mcp-profiles/boxie.json — mcp-config passed through
• pai unknowncmd — still errors with "Unknown command"
• pai --model opus — passed through correctly
• Existing flags (-r, -m, -l, --safe) still work as before